An investigation into last year's fatal Virgin Galactic crash has found that human error as the direct cause, but pointed to a number of shortcomings in preparation that may have contributed to the accident.
In a briefing, America's National Transportation Safety Board (NTSB) said co-pilot Michael Alsbury, 39 - who was killed in the accident - had prematurely repositioned the spacecraft's tail wings, a process known as "unlocking" the feather.
While human error was identified as the direct cause, the NTSB report found contractors Scaled Composites - who designed and manufactured the spacecraft - had not properly considered that such a human mistake could happen.
The report found that the co-pilot had to make decisions at high speed, while being exposed to a number of "stressors" such as intense vibrations from the craft.
Officials added that the Alsbury - who had previously been praised as "as professional a co-pilot as you could have" - also had more work to do on the test flight than had been done in earlier preparations.
These factors had not been thoroughly prepared for in simulation, investigators said, with the SpaceShipTwo pilots even wearing different gear in test flight to that worn during simulation.
The spacecraft crashed over the Mojave Desert in southern California in October last year. Pilot Peter Siebold, 43, was also seriously hurt in the accident.
The remains of SpaceShipTwo were spread over five miles, leaving investigators with the huge task of scouring the area to ensure every piece of debris could be documented and examined.
Richard Branson's space tourism company - which promises trips outside the Earth's atmosphere and back for six people at a time - defended its safety record following the accident.
In a video statement, Sir Richard Branson said the report proved that the "spaceship Scaled Composites had designed, built and then flew for us was performing exactly as it should have".
He also said paid tribute to the "tragic and brave sacrifice" of Alsbury, and said: "Our thoughts go out again today to the family, friends and colleagues of Mike."
He added that Alsbury and Siebold's efforts would drive Virgin Galactic on to reach space.
"Their tremendous efforts are not in vain and will serve to strengthen our resolve to make big dreams come true," he said.